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Multi-site hosting with Application Gateway for Containers - Gateway API

  • Article

This document helps you set up an example application that uses the resources from Gateway API to demonstrate hosting multiple sites on the same Kubernetes Gateway resource / Application Gateway for Containers frontend. Steps are provided to:

  • Create a Gateway resource with one HTTP listener.
  • Create two HTTPRoute resources that each reference a unique backend service.

Background

Application Gateway for Containers enables multi-site hosting by allowing you to configure more than one web application on the same port. Two or more unique sites can be hosted using unique backend services. See the following example scenario:

A figure showing multisite hosting with Application Gateway for Containers.

Prerequisites

  1. If you used the BYO deployment strategy, ensure you set up your Application Gateway for Containers resources and ALB Controller.

  2. If you used the ALB managed deployment strategy, ensure provisioning of your ALB Controller and the Application Gateway for Containers resources via the ApplicationLoadBalancer custom resource.

  3. Deploy sample HTTP application:
    Apply the following deployment.yaml file on your cluster to create a sample web application to demonstrate path, query, and header based routing.

    kubectl apply -f https://raw.githubusercontent.com/MicrosoftDocs/azure-docs/refs/heads/main/articles/application-gateway/for-containers/examples/traffic-split-scenario/deployment.yaml

    This command creates the following on your cluster:

    • A namespace called test-infra
    • Two services called backend-v1 and backend-v2 in the test-infra namespace
    • Two deployments called backend-v1 and backend-v2 in the test-infra namespace

Deploy the required Gateway API resources

  1. Create a Gateway
kubectl apply -f - <<EOF
apiVersion: gateway.networking.k8s.io/v1
kind: Gateway
metadata:
  name: gateway-01
  namespace: test-infra
  annotations:
    alb.networking.azure.io/alb-namespace: alb-test-infra
    alb.networking.azure.io/alb-name: alb-test
spec:
  gatewayClassName: azure-alb-external
  listeners:
  - name: http-listener
    port: 80
    protocol: HTTP
    allowedRoutes:
      namespaces:
        from: Same
EOF

Note

When the ALB Controller creates the Application Gateway for Containers resources in ARM, it'll use the following naming convention for a frontend resource: fe-<8 randomly generated characters>

If you would like to change the name of the frontend created in Azure, consider following the bring your own deployment strategy.

Once the gateway resource is created, ensure the status is valid, the listener is Programmed, and an address is assigned to the gateway.

kubectl get gateway gateway-01 -n test-infra -o yaml

Example output of successful gateway creation.

status:
  addresses:
  - type: Hostname
    value: xxxx.yyyy.alb.azure.com
  conditions:
  - lastTransitionTime: "2023-06-19T21:04:55Z"
    message: Valid Gateway
    observedGeneration: 1
    reason: Accepted
    status: "True"
    type: Accepted
  - lastTransitionTime: "2023-06-19T21:04:55Z"
    message: Application Gateway For Containers resource has been successfully updated.
    observedGeneration: 1
    reason: Programmed
    status: "True"
    type: Programmed
  listeners:
  - attachedRoutes: 0
    conditions:
    - lastTransitionTime: "2023-06-19T21:04:55Z"
      message: ""
      observedGeneration: 1
      reason: ResolvedRefs
      status: "True"
      type: ResolvedRefs
    - lastTransitionTime: "2023-06-19T21:04:55Z"
      message: Listener is accepted
      observedGeneration: 1
      reason: Accepted
      status: "True"
      type: Accepted
    - lastTransitionTime: "2023-06-19T21:04:55Z"
      message: Application Gateway For Containers resource has been successfully updated.
      observedGeneration: 1
      reason: Programmed
      status: "True"
      type: Programmed
    name: https-listener
    supportedKinds:
    - group: gateway.networking.k8s.io
      kind: HTTPRoute

Once the gateway is created, create two HTTPRoute resources for contoso.com and fabrikam.com domain names. Each domain forwards traffic to a different backend service.

kubectl apply -f - <<EOF
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: contoso-route
  namespace: test-infra
spec:
  parentRefs:
  - name: gateway-01
  hostnames:
  - "contoso.com"
  rules:
  - backendRefs:
    - name: backend-v1
      port: 8080
---
apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: fabrikam-route
  namespace: test-infra
spec:
  parentRefs:
  - name: gateway-01
  hostnames:
  - "fabrikam.com"
  rules:
  - backendRefs:
    - name: backend-v2
      port: 8080
EOF

Once the HTTPRoute resource is created, ensure both HTTPRoute resources show Accepted and the Application Gateway for Containers resource is Programmed.

kubectl get httproute contoso-route -n test-infra -o yaml
kubectl get httproute fabrikam-route -n test-infra -o yaml

Verify the status of the Application Gateway for Containers resource is successfully updated for each HTTPRoute.

status:
  parents:
  - conditions:
    - lastTransitionTime: "2023-06-19T22:18:23Z"
      message: ""
      observedGeneration: 1
      reason: ResolvedRefs
      status: "True"
      type: ResolvedRefs
    - lastTransitionTime: "2023-06-19T22:18:23Z"
      message: Route is Accepted
      observedGeneration: 1
      reason: Accepted
      status: "True"
      type: Accepted
    - lastTransitionTime: "2023-06-19T22:18:23Z"
      message: Application Gateway For Containers resource has been successfully updated.
      observedGeneration: 1
      reason: Programmed
      status: "True"
      type: Programmed
    controllerName: alb.networking.azure.io/alb-controller
    parentRef:
      group: gateway.networking.k8s.io
      kind: Gateway
      name: gateway-01
      namespace: test-infra

Test access to the application

Now we're ready to send some traffic to our sample application, via the FQDN assigned to the frontend. Use the following command to get the FQDN.

fqdn=$(kubectl get gateway gateway-01 -n test-infra -o jsonpath='{.status.addresses[0].value}')

If you specify the server name indicator using the curl command, contoso.com for the frontend FQDN, it returns a response from the backend-v1 service.

fqdnIp=$(dig +short $fqdn)
curl -k --resolve contoso.com:80:$fqdnIp http://contoso.com

Via the response we should see:

{
 "path": "/",
 "host": "contoso.com",
 "method": "GET",
 "proto": "HTTP/1.1",
 "headers": {
  "Accept": [
   "*/*"
  ],
  "User-Agent": [
   "curl/7.81.0"
  ],
  "X-Forwarded-For": [
   "xxx.xxx.xxx.xxx"
  ],
  "X-Forwarded-Proto": [
   "http"
  ],
  "X-Request-Id": [
   "dcd4bcad-ea43-4fb6-948e-a906380dcd6d"
  ]
 },
 "namespace": "test-infra",
 "ingress": "",
 "service": "",
 "pod": "backend-v1-5b8fd96959-f59mm"
}

If you specify the server name indicator using the curl command, fabrikam.com for the frontend FQDN, it returns a response from the backend-v1 service.

fqdnIp=$(dig +short $fqdn)
curl -k --resolve fabrikam.com:80:$fqdnIp http://fabrikam.com

Via the response we should see:

{
 "path": "/",
 "host": "fabrikam.com",
 "method": "GET",
 "proto": "HTTP/1.1",
 "headers": {
  "Accept": [
   "*/*"
  ],
  "User-Agent": [
   "curl/7.81.0"
  ],
  "X-Forwarded-For": [
   "xxx.xxx.xxx.xxx"
  ],
  "X-Forwarded-Proto": [
   "http"
  ],
  "X-Request-Id": [
   "adae8cc1-8030-4d95-9e05-237dd4e3941b"
  ]
 },
 "namespace": "test-infra",
 "ingress": "",
 "service": "",
 "pod": "backend-v2-594bd59865-ppv9w"
}

Congratulations, you have installed ALB Controller, deployed a backend application and routed traffic to two different backend services via different hostnames via Gateway API on Application Gateway for Containers.